A lithographic apparatus is a machine constructed to apply a desired pattern onto a substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). A lithographic apparatus may for example project a pattern from a patterning device (e.g. a mask or reticle) onto a layer of radiation-sensitive material (resist) provided on a substrate.
The wavelength of radiation used by a lithographic apparatus to project a pattern onto a substrate typically determines the minimum size of features which can be formed on that substrate. A lithographic apparatus which uses EUV radiation, being electromagnetic radiation having a wavelength within the range of about 4 nm to about 20 nm, may be used to form smaller features on a substrate than a conventional lithographic apparatus (which may, for example, use electromagnetic radiation with a wavelength of 193 nm).
EUV radiation for use by a lithographic apparatus is generated by a source which may for example be a laser produced plasma (LPP) source. A laser, for example a CO2 laser, may be arranged to deposit energy into a fuel, for example tin (Sn), to generate the LPP. Radiation, including EUV radiation for use by the lithographic apparatus, is emitted from the plasma during de-excitation and recombination of ions of the plasma.